Planar directed light source

ABSTRACT

A solid-state light source includes a planar substrate, a single unitary organic light emitting diode (OLED) layer deposited on the planar substrate, the organic light emitting diode layer including first and second electrodes for providing electrical power to the OLED layer, an encapsulating cover covering the OLED layer; first and second conductors electrically connected to the first and second electrodes, and extending beyond the encapsulating cover for making electrical contact to the first and second electrodes by an external power source; and a lenslet array located on the substrate and/or encapsulating cover and coextensive with the OLED layer for directing the light emitted by the OLED layer.

FIELD OF THE INVENTION

The present invention relates to the use of organic light emittingdiodes for area illumination, and more particularly to directed areaillumination such as is provided by a spotlight.

BACKGROUND OF THE INVENTION

The light emitting elements in conventional bulbs (the filament of anincandescent bulb or the fluorescent material in a fluorescent bulb) areextremely bright and emit light in every direction. In manyapplications, directed lighting is preferred, for example withspotlights, floodlights, or track lighting. For these applications,traditional lighting devices such as incandescent or fluorescent lightbulbs typically require reflectors or lenses to direct the light output.For example, desk, table, floor and ceiling lamps conventionally useshades to reflect light to the ceiling or floor to provide indirectlighting suitable for use in a home or office environment. Spotlights orfloodlights place the lighting element within a curved reflector todirect the light. Thick glass conventional lenses and fresnel lenses areoften employed to both refractively direct the light emitted and to sealthe lighting elements. These reflectors and lenses are expensive, may beheavy, and take considerable space.

Solid-state lighting devices made of light emitting diodes areincreasingly useful for applications requiring robustness and long-life.For example, solid-state LEDs are found today in automotiveapplications. These devices are typically formed by combining multiple,small LED devices providing a point light source into a single moduletogether with glass lenses or reflectors suitably designed to direct thelight as is desired for a particular application; see for example,WO99/57945, published Nov. 11, 1999. These multiple devices areexpensive and complex to manufacture and integrate into singleillumination devices.

Organic light emitting diodes (OLEDs) are manufactured by depositingorganic semiconductor materials between electrodes on a substrate. Thisprocess enables the creation of light sources having an extended lightemitting surface area on a single substrate. The prior art describes theuse of electro-luminescent materials as adjuncts to conventionallighting; see for example U.S. Pat. No. 6,168,282, issued Jan. 2, 2001to Chien. In this case, because of the limited light output from theelectro-luminescent material, it is not useful for primary lighting.

EP1120838A2, published Aug. 1, 2001 describes a method for mountingmultiple organic light emitting devices on a mounting substrate tocreate a light source. However, the light source is not directed.

There is a need therefore for an improved OLED lighting apparatus fordirected illumination having a simple construction that provides ahighly integrated and robust light.

SUMMARY OF THE INVENTION

The need is met by providing a solid-state area illumination lightsource that includes a planar substrate, a non-pixellated organic lightemitting diode (OLED) layer deposited on the planar substrate, theorganic light emitting diode layer including first and second electrodesfor providing electrical power to the OLED layer, an encapsulating covercovering the OLED layer; first and second conductors electricallyconnected to the first and second electrodes, and extending beyond theencapsulating cover for making electrical contact to the first andsecond electrodes by an external power source; and a lenslet arraylocated on the substrate and/or encapsulating cover and coextensive withthe OLED layer for directing the light emitted by the OLED layer.

ADVANTAGES

The present invention has the advantage of providing an inexpensive,long lived, highly efficient, lightweight, low volume directed lightsource that provides directed illumination in a small package.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a partial cross section of a prior art conventionalOLED illumination device;

FIG. 2 is a partial cross section of a solid-state area illuminationlight source according to one embodiment of the present invention;

FIG. 3 is a perspective view of the light source shown in FIG. 2;

FIG. 4 is a cross sectional view of an area illumination light sourceaccording to the present invention that emits light through both asubstrate and a cover;

FIG. 5 is a cross sectional view of an area illumination light sourceaccording to the present invention that emits light through a substrate;

FIG. 6 is a cross sectional view of an area illumination light sourceaccording to the present invention that emits light through a cover;

FIG. 7 is a cross sectional view of an area illumination light sourceaccording to an alternative embodiment of the present invention;

FIG. 8 is a partial perspective view of a lenslet array having pyramidallenslets useful with the present invention; and

FIG. 9 is a partial perspective view of a lenslet array having conicallenslets useful with the present invention.

It will be understood that the figures are not to scale since theindividual layers are too thin and the thickness differences of variouslayers too great to permit depiction to scale.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of a prior art non-pixellated OLED lightsource including an organic light emitting layer 12 disposed between twoelectrodes, e.g. a cathode 14 and an anode 16. The organic lightemitting layer 12 emits light upon application of a voltage from a powersource 18 across the electrodes. The OLED light source 10 typicallyincludes a substrate 20 such as glass or plastic. It will be understoodthat the relative locations of the anode 16 and cathode 14 may bereversed with respect to the substrate. The term OLED light sourcerefers to the combination of the organic light emitting layer 12, thecathode 14, the anode 16, and other layers described below. As usedherein the term “non-pixellated” means that the organic light emittinglayer 12 is not divided into many small sub-sections or pixels that canbe independently activated to form an image. It is contemplated howeverthat the term non-pixellated includes light emitting layers that may bedivided into a relatively small number of segments (e.g. fewer than 10)for purposes such as providing reliability, adjustable levels ofillumination, or adjustable color output.

Referring to FIG. 2, a perspective view of a directed area illuminationlight source (e.g. a spotlight) according to one embodiment of thepresent invention is shown. The lighting source includes anon-pixellated OLED light source 10 of the type shown in FIG. 1 having alenslet array 11, that directs the light 13 emitted from the lightsource. The lenslet array may also function as the substrate 20 (asshown) or cover 22. When power is supplied to the light source 10, itemits light uniformly from the entire OLED light emitting layer 12. Thelight is emitted in all directions from the light emitting layer 12.When the light passes through the lenslet array 11, it is concentratedin a desired direction.

Referring to FIG. 3, according to one embodiment of the presentinvention, the light source 10, includes a substrate 20, the substratedefining a light emissive area portion 20′ and an extension 20″. Anorganic light emitting layer 12 is disposed between a cathode 14 and ananode 16. An encapsulating cover 22 is provided over the light source 10on the body portion 20′ of the substrate 20. To minimize cost ofmanufacture, assembly, and design and to maximize the robustness of thelight source 10, according to the present invention, the materials aredeposited as a single unitary coating onto a single unitary substrate20.

The cover 22 may be a separate element such as a hermetically sealedcover plate affixed over the layers 12, 14, and 16 or the cover may becoated over the layers 12, 14, and 16 as an additional layer. The OLEDlight emitting layer 12 is continuous over the substrate to provide acontinuous light emitting area. First and second conductors 24 and 26located on the substrate 20 are electrically connected to the first andsecond electrodes 14 and 16, and extend beyond the encapsulating cover22 on extension 20″ for making electrical contact to the first andsecond electrodes by an external power source (not shown). This powersource may be mounted in a portable apparatus that includes the lightsource 10 (as in a flashlight) or separately connected through a socket34 to a power cable 46. The cable may be detachable from the lightsource or permanently affixed.

To allow light to be emitted from the OLED light source 10, thesubstrate 20, the electrodes 14 and 16, and the cover 22 aretransparent. In applications where it is not required to emit light fromboth sides of the substrate, one or more of the substrate, cover, anode,or cathode may be opaque or reflective. The substrate 20 and/or cover 22may be suitably treated to provide directional lighting in one directiononly. For example, the cover, substrate, or one of the electrodes may beprovided with a reflective surface so that light emitted by the OLEDlayer will travel through the other surface and the device will emitlight from only one side.

Referring to FIG. 4, in one embodiment, the light source 10 has noreflective layers and light 13 is emitted through both the encapsulatingcover 22 and the substrate 20. Both the encapsulating cover 22 and thesubstrate 20 have an embossed or molded lenslet array 11. Referring toFIG. 5, in an alternative embodiment, the encapsulating cover 22includes a reflective layer 23 and light 13 is directed through thesubstrate 20 which includes a lenslet array 11. Referring to FIG. 6, ina further alternative embodiment, the electrode deposited on thesubstrate 20 is reflective and light 13 is emitted through theencapsulating cover 22 which includes an embossed or molded lensletarray 11. Referring to FIG. 7, in a still further alternativeembodiment, lenslet arrays 11 are provided by laminating a lenslet sheet27 onto the encapsulating cover 22 and/or the substrate 20. The lensletsheet may be attached using an index matching optical adhesive. In thiscase, the lenslet array is located farther away from the light emittinglayer 12, and the focal length of the lenslets is adjusted accordinglyto locate the focal points at the light emitting layer 12.

The lenslet array 11 may take a variety of forms depending on theapplication desired. In a preferred embodiment, the lenslet array is aflat layer embossed or molded on either or both the substrate 20 and/orthe encapsulating cover 22. In one embodiment, the lenslet array iscoextensive with the light emitting layer 12 of the device. For example,a multiplicity of separate lenses may be embossed or molded into thecover and/or the substrate. In an alternative embodiment, the lensletsare embossed into a separate layer, for example a plastic sheet, whichis applied to the substrate and/or encapsulating cover over the lightemitting area. The lenslets may be identical across the array orelements at the edge may differ from those in the center to furtherdirect the light in a preferred way.

As a general rule, the focal length of a short focal length lens is onthe order of its diameter. In the present invention, the lensletarray(s) is applied directly to the substrate and/or cover of the lightemitters. In an OLED lamp, this distance can be as small as amillimeter. The lenslet arrays should have a similar focal length and beas small as possible, a millimeter or less. The shape of the lensletarrays can vary depending on the desired application, for exampleconventional convex lenses, pyramids 36 (as shown in FIG. 8), and cones38 (as shown in FIG. 9).

Because both the lenslet arrays 11 and the OLED light source 10 areflat, the present invention enables a very flat area illumination lightsource that directs light in a preferred way.

The substrate 20 can be either rigid or flexible. Rigid substrates, suchas glass, provide more structural strength and are generally planar andmay have a variety of shapes other than rectangular. The presentinvention may also be used with a flexible substrate, such as plastic.If a flexible substrate is used, the flexible transparent substrate maybe attached to a rigid support or held within a frame. The frame may beopaque or transparent depending on the lighting and decorating needs ofthe application.

The present invention may be powered by a variety of sources, forexample from standard AC power (such as 110 volts AC or 220 volts AC)available in households or offices. If necessary, conventional powerconversion devices may be employed to provide power suitable for used bythe light emitting layer 12. Alternatively, DC sources found in vehiclesor through batteries may be used, for example 24, 12, or 6 volt DCsources with appropriate converters to obtain a desired operatingvoltage and waveform.

The present invention has the added advantage that the directed lightsource has a compact planar configuration enabling efficient storage,packing, and shipping.

In a preferred embodiment, the invention is employed in an areaillumination device that includes an Organic Light Emitting Diode (OLED)which is composed of small molecule or polymeric OLED materials asdisclosed in but not limited to U.S. Pat. No. 4,769,292, issued Sep. 6,1988 to Tang et al., and U.S. Pat. No. 5,061,569, issued Oct. 29, 1991to VanSlyke et al. The light source may also include multiple lightemitting layers as described in commonly assigned U.S. patentapplication Ser. No. 10/231,853 filed Aug. 7, 2002 by Tyan now U.S. Pat.No. 6,693.296), and U.S. Ser. No. 10/077,270 filed Feb. 15, 2002 by Liaoet al., the disclosures of which are incorporated herein by reference.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST 10 OLED light source 11 lenslet array 12 organic lightemitting layer 13 directed light 14 cathode 16 anode 18 power source 20substrate 20′ light emissive portion of substrate 20″ extension ofsubstrate 22 encapsulating cover 23 reflective layer 24 first conductor26 second conductor 27 sheet having lenslet array 34 socket 36 pyramidallenslet 38 conical lenslet 46 power cable

1. A solid-state area illumination light source, comprising: a) a planarsubstrate, b) a non-pixellated organic light emitting diode (OLED) layerdeposited on the planar substrate, the organic light emitting diodelayer including first and second electrodes for providing electricalpower to the OLED layer, c) an encapsulating cover covering the OLEDlayer; d) first and second conductors electrically connected to thefirst and second electrodes, and extending beyond the encapsulatingcover for making electrical contact to the first and second electrodesby an external power source; and e) a lenslet array located on theencapsulating cover and coextensive with the OLED layer for directingthe light emitted by the OLED layer, wherein the encapsulating cover istransparent, and light is emitted from the OLED layer through theencapsulating cover.
 2. The solid-state light source claimed in claim 1,wherein the lenslet array is formed in the encapsulating cover.
 3. Thesolid-state light source claimed in claim 1, wherein the lenslet arrayis attached to the encapsulating cover by an optical adhesive.
 4. Thelight source claimed in claim 1, wherein the substrate is a rigid planarsubstrate.
 5. The light source claimed in claim 1, wherein the substrateis flexible.
 6. The light source claimed in claim 5, further comprisinga support for holding the substrate in a plane.
 7. The lightingapparatus claimed in claim 1, wherein the lenslet array is embossed. 8.The lighting apparatus claimed in claim 1, wherein the lenslet array ismolded.
 9. The light source claimed in claim 1, wherein the cover is ahermetically sealed cover plate.
 10. The light source claimed in claim1, wherein the cover is a coated layer.
 11. The lighting apparatusclaimed in claim 1, wherein the light source operates on standard power.12. The lighting apparatus claimed in claim 1, wherein the planarsubstrate is transparent.
 13. The lighting apparatus claimed in claim 1,wherein the planar substrate is transparent, and light is emitted fromthe OLED layer through the encapsulating cover and through the planarsubstrate.
 14. The lighting apparatus claimed in claim 1, wherein theOLED layer emits light through the encapsulating cover and furtherincludes a reflective layer between the light emitter and the substrate.15. The light source claimed in claim 13, wherein a lenslet array islocated on each of the substrate and the cover.
 16. The light sourceclaimed in claim 1, wherein the lenslets are hemispheres.
 17. The lightsource claimed in claim 1, wherein the lenslets are pyramids.
 18. Thelight source claimed in claim 1, wherein the lenslets are cones.
 19. Thelight source claimed in claim 1, wherein the lenslets are fresnellenslets.
 20. The light source claimed in claim 1, wherein the lensletshave a focal length less than 1 mm, and are arranged such that theirfocal point is located at the light emitting layer.